1. Field of the Invention
The invention relates to an electrochemical storage cell based on sodium and sulphur, including an anode compartment and a cathode compartment being separated from one another by an alkali metal ion-conductive solid electrolyte and being at least zonally bounded by a metallic casing, and a closure of the storage cell having a retention element being connected to the casing and on which an insulating ring fastened to the solid electrolyte is retained.
Such electrochemical storage cells are highly suitable as energy sources. They are used to an increased extent in the construction of high-power batteries which are provided for the power supply of electric vehicles. Examples thereof are storage cells based on sodium and sulphur, which are rechargeable and have a solid electrolyte made of beta-alumina which separates the anode compartment of the storage cell from the cathode compartment. The storage cell is closed on the outside by sealing elements which are disposed overlappingly and cover the anode compartment and the cathode compartment. Between the sealing elements, a ceramic ring of alpha-alumina is additionally disposed and is firmly connected to the solid electrolyte. The two sealing elements are made out of metal. Aluminum is preferably used for their production in that case. The sealing elements are permanently connected to the ring made of alpha-alumina by means of thermocompression. The drawback of such a device is that, in the event of damage to the closure, sodium, sulphur or sodium polysulphide can flow out of the storage cell. Destruction of the closure can, for example, be caused by strong exothermic reactions inside the storage cell or detachment of the ring made of alpha-alumina from the solid electrolyte. Such a detachment will be caused by corrosion of the glass with which the alpha-alumina ring is connected to the solid electrolyte. Faulty connections between the metallic sealing elements and the ceramic ring can also be the cause thereof.
2. Summary of the Invention
It is accordingly an object of the invention to provide an electrochemical storage cell, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type cell and which has an improved closure.
With the foregoing and other objects in view there is provided, in accordance with the invention, an electrochemical storage cell, based on sodium and sulphur, comprising an anode compartment; a cathode compartment; an alkali metal ion-conductive solid electrolyte separating the anode and cathode compartments from each other; a metallic casing at least zonally bounding the anode and cathode compartments; and a closure for the storage cell having a retention element connected to the casing, an insulating ring retained on the retention element and fastened to the solid electrolyte, and an additional seal.
In accordance with another feature of the invention, the additional seal is formed by two overlapping sealing elements, between which an insulating ring made of ceramic is disposed.
In accordance with a further feature of the invention, the first sealing element is fastened indirectly or directly on the casing, and the second sealing element is fastened on the rod-shaped current collector.
In accordance with an added feature of the invention, the sealing elements are formed as annular discs and are provided with cylindrical appendage elements for the purpose of fastening on the casing and on the current collector, respectively.
In accordance with an additional feature of the invention, the dimensions of the two sealing elements are chosen in such a way that a space between the casing and the rod-shaped current collector is fully covered and externally closed in a leak-proof and gas-tight manner by the insulating ring between the two sealing elements.
In accordance with yet another feature of the invention, the rod-shaped current collector has an outer surface, and the cylindrical appendage of one of the sealing elements zonally encloses and is permanently connected to the outer surface of the rod-shaped current collector.
In accordance with yet a further feature of the invention, the retention element has an inner surface, and the cylindrical appendage of one of the sealing elements is permanently fastened on the inner surface of the retention element.
In accordance with yet an added feature of the invention, the other insulating ring disposed between the two sealing elements is made of alpha-alumina and is connected gas-tightly to the two sealing elements.
In accordance with yet an additional feature of the invention, the insulating ring fastened on the solid electrolyte has a diameter being at least equal to the diameter of the other insulating ring.
In an alternative embodiment of the storage cell of the invention, the two sealing elements are formed by an inwardly pointing flange of an extension fastened on the casing and a sealing element which is also fastened on the current collector. The length of the flange and of the sealing element is chosen to be large enough for the two components to overlap. In this region an insulating ring is also disposed between the flange and the sealing element and is connected by thermocompression to these two components. The sealing elements are made out of aluminum and the insulating rings are made out of alpha-alumina.
In accordance with again another feature of the invention, there is provided a current collector, the additional seal having a first sealing element formed as a flange, a second sealing element formed as an annular disc fastened on the current collector and another insulating ring disposed between the flange and the annular disc, the first and second sealing elements zonally overlapping.
In accordance with again a further feature of the invention, there is provided a cylindrical extension of the casing having first and second ends, the flange pointing into the casing and being located on the second end of the cylindrical extension, and the first end of the cylindrical extension also having a flange pointing into the casing.
In accordance with again an added feature of the invention, the current collector has an outer surface, and the second sealing element is a retention element having a cylindrical appendage zonally surrounding and being fastened on the outer surface of the current collector.
In accordance with again an additional feature of the invention, the insulating ring disposed between the flange and the retention element is made of alpha-alumina, and including one annular aluminum disc interposed between the insulating ring and the flange and another annular aluminum disc interposed between the insulating ring and the retention element, the insulating ring being permanently connected to the flange and to the retention element by thermocompression.
In accordance with still another feature of the invention, there is provided one annular aluminum disc interposed between the insulating ring on the retention element and the flange of the extension and another annular aluminum disc interposed between the insulating ring on the retention element and the retention element, the insulating ring on the retention element being permanently connected to the flange of the extension and to the retention element by thermocompression.
In accordance with a concomitant feature of the invention, the cylindrical extension has an inner surface, the insulating ring on the retention element extends up to the inner surface of the cylindrical extension, and the insulating ring of the additional seal has a width being at most equal to the width of the insulating ring on the retention element.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an electrochemical storage cell, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.